Update readme (#269)

* Fix compiler warning

'MyLambda' was identified as an executable target given the presence of a 'main.swift' file. Starting with tools version 5.4.0 executable targets should be declared as 'executableTarget()'

* Fix package dependency for swift-aws-lambda-events

The swift-aws-lambda-events repo has not yet pushed tag 0.1.0 so the build fails, see output from swift build:

Computing version for https://github.com/swift-server/swift-aws-lambda-events.git
error: Dependencies could not be resolved because no versions of 'swift-aws-lambda-events' match the requirement 0.1.0..<1.0.0 and root depends on 'swift-aws-lambda-events' 0.1.0..<1.0.0.

This commit adds the workaround mentioned in the issue for the missing tag awslabs/swift-aws-lambda-events#3

* Fix multiple products and targets build error

Author: sja26

readme.md

@@ -30,7 +30,7 @@ First, create a SwiftPM project and pull Swift AWS Lambda Runtime as dependency
          .package(url: "https://github.com/swift-server/swift-aws-lambda-runtime.git", from: "0.1.0"),
      ],
      targets: [
-         .target(name: "MyLambda", dependencies: [
+         .executableTarget(name: "MyLambda", dependencies: [
            .product(name: "AWSLambdaRuntime", package: "swift-aws-lambda-runtime"),
          ]),
      ]
@@ -91,12 +91,11 @@ First, add a dependency on the event packages:
      ],
      dependencies: [
          .package(url: "https://github.com/swift-server/swift-aws-lambda-runtime.git", from: "0.1.0"),
-         .package(url: "https://github.com/swift-server/swift-aws-lambda-events.git", from: "0.1.0"),
      ],
      targets: [
-         .target(name: "MyLambda", dependencies: [
+         .executableTarget(name: "MyLambda", dependencies: [
            .product(name: "AWSLambdaRuntime", package: "swift-aws-lambda-runtime"),
-           .product(name: "AWSLambdaEvents", package: "swift-aws-lambda-events"),
+           .product(name: "AWSLambdaEvents", package: "swift-aws-lambda-runtime"),
          ]),
      ]
  )